This invention relates to distributed voice/data/image switching systems and more particularly to circuitry for dynamic allocation of bandwidth and circuit paths between switching nodes in a ring communication system.
In recent years a number of local area network (LAN) technologies have developed which allow for interconnection of a large number of data devices on a contention basis. Shared resources on the local area network are typically called servers; e.g., print servers, file servers, or communication servers. Conceptually, the present invention may be considered a system of distributed switching servers that may employ several different means for affecting internodal communication. Two of the embodiments described employ the services of a local area network: one uses a baseband bus LAN, and another employs an integrated token ring LAN. In a third embodiment, control of internodal communications may be affected by common signaling channels within the network signal stream.
The advantages of distributed switching are well known: e.g., improved reliability, improved availability, improved survivability, and reduced installation in wiring costs. However, a fundamental obstacle has prevented the widespread adoption of distributed switching, that obstacle being connectivity or allocation of circuit paths among the various nodes of the network.
Most present day switching systems employ star architectures or distributed star architectures. In the star architecture, a large central switch is employed and all stations are wired to a central location; the wiring cost is high and survivability low. A distributed star still employs a large central switch but reduces the wiring requirements by multiplexing many conversations or circuit paths onto the wiring between the central switch and peripheral switching units. The connectivity between peripheral switching units is limited to the number of circuit paths carried on the multiplexed wiring between the central switch and the peripheral switching units (PSU). Connectivity is not a problem when the switch is non-blocked, i.e. there is a circuit path for every station in the system. However, in many cases the cost of a non-blocked system is excessive and some level of blocking is introduced in order to reduce the cost per station of the system.
In the distributed star, blocking may be introduced in the PSU. Consequently, all stations on the PSU may contend for the number of circuits that exist between the PSU and the central switch. Typically the number of calls initiated per unit time varies from one PSU to another. To obtain a desired grade of service, i.e. the likelihood that a circuit path will be available for a call, it is thus necessary to balance the load on the PSU's by physically changing the number of telephones wired thereto. Because of the dynamic nature of modern businesses, the offered load to each PSU changes with time necessitating an ongoing process of traffic analysis followed by physically disconnecting and reconnecting telephones from one PSU to another. That process is both costly and time consuming.
To ensure a fixed grade of service requires a significantly larger ratio of circuits to telephone sets (telesets) when the number of circuits is small. Therefore, a more desirable system would allow the number of circuits per PSU to vary dynamically in accordance with the number of associated telesets. Ideally, the system would allow for the offered load from a local station to contend for all the circuits of the central switch rather than to contend for the small and fixed number of circuits at an individual PCU. The invention herein described addresses these issues and problems.
It is therefore a general object of this invention to provide distributed voice, data, and image PBX communications in a form that solves the limited connectivity problem found in present day systems.
A further object of this invention is to integrate important aspects of voice, data, and image communications into a single distributed system that provides means to accomplish: single and multi-party voice connections both intrasystem and to the public switched voice network; point-to-point, multipoint, and loop data connections; terminal concentration to local area networks; terminal concentration to public packet data networks; modem pooling; digital video switching; wide-area networking; and gateways between local and/or wide area networks.
It is a further object of the invention to provide a modular system that permits growth from a small single node system to a multinode system with essentially uniform cost per line or port.
It is another object of the invention to provide a system that may be configured with either blocking or non-blocking service both at the system and individual resource levels.
It is a further object of this invention to provide a system having the capability to allow the traffic load to be offered to the pool of traffic capacity at the highest network level when a system is configured for blocking service.
It is another object of this invention to provide a system that allows variable bandwidth switching between the nodes of the distributed switch so as to maximize the total traffic capacity in an integrated voice, data, and digital video environment.
It is a further object of this invention to provide a system that combines circuit switching and local area network packet switching so as to present the user with the best capabilities of both types of systems, thus allowing the system to be configured to the specific requirements of each application.
It is another object of this invention to provide a system having the flexibility to be dynamically configured in various commonly used data communications connection topologies: point-to-point, multipoint and loop.